Conventionally, there is a method referred to as sputtering, as a method for forming a thin film on the surface of a silicon substrate, a resin substrate, a ceramic substrate, or the like.
In the sputtering, for example, in a state where a target made of a predetermined material is arranged to face the substrate in a vacuum container, a discharge gas is introduced into the vacuum container, and a plasma is generated by applying an electric field between the substrate and the target. Thereby, atoms or molecules are discharged from the target by making positive ions of the plasma collide with the target. Then, the thin film is formed by making the discharged atoms introduced and deposited onto the surface of the substrate.
Conventionally, electrode structures of various systems have been proposed for the system which forms a thin film by the sputtering (hereinafter referred to as sputtering system). Among the electrode structures, an electrode structure of a magnetron system has been industrially most frequently used. The sputtering system to which the magnetron system is applied, is capable of generating a high density plasma on the target in such a manner that electrons discharged from the cathode are made to perform a trochoid movement by applying a magnetic field intersecting the electric field. This makes it possible to enhance the sputtering rate by a relatively low voltage and to increase the forming rate of the thin film.
Conventionally, there are various types of the electrode structure of the magnetron system, but the type which is industrially most useful and common is, for example, an electrode structure referred to as a planar magnetron cathode electrode provided with a target having a planar shape, as shown in FIG. 22 and FIG. 23. In the planar magnetron cathode electrode, for example, as shown in FIG. 23, an S pole 102 of a magnet is provided near the center of the back surface side of the target 8, that is, the back surface side of the surface facing the substrate 6, and an N pole 101 of the magnet is provided in the outer peripheral part of the target 8. At this time, the magnetic field as shown in FIG. 22 is generated on the target 8, which causes an electron to perform the trochoid movement.
At this time, the trochoid movement of electron is caused in the vicinity where the magnetic field (line of magnetic force) is orthogonal to the electric field E, as shown in FIG. 24. Thereby, as shown in FIG. 25, in the region MC where the magnetic field (line of magnetic force) is orthogonal to the electric field, more atoms or molecules are discharged so that the consumption rate of the target 8 is increased as compared with the other parts. Further, at this time, in the region MC where the magnetic field (line of magnetic force) is orthogonal to the electric field E, more atoms or molecules are discharged, and hence in a film 8′ formed on the surface of the substrate 6, as shown in FIG. 25, a variation arises between the film thickness of the part facing the region MC where the magnetic field (line of magnetic force) is orthogonal to the electric field E, and the film thickness of the other parts.
Further, in recent years, for example, there are proposed a method which reduces the variation of film thickness by temporally changing the region where the magnetic field (line of magnetic force) is orthogonal to the electric field, by rotating the magnet (see, for example, Patent Document 1), and a method in which the magnet is formed into a complicated shape so that the region where the magnetic field (line of magnetic force) is orthogonal to the electric field is made uniform (see, for example, Patent Document 2).    Patent Document 1: Japanese Patent Laid-Open No. 7-292468    Patent Document 2: Japanese Patent No. 2505724
A problem to be solved by the present invention is, as explained in the background art, that in the sputtering system using the planar magnetron cathode electrode, it is difficult to reduce the inhomogeneity and the film thickness nonuniformity of a thin film formed on the substrate, which are caused by the nonuniform ion collision on the target surface, and the nonuniform spatial density distribution of the plasma, that is, the difference in the amount of discharged atoms or molecules of the target between the vicinity where the magnetic field (line of magnetic force) is orthogonal to the electric field and the other regions.
Further, as methods for solving the problem, for example, there are proposed the methods as described in Patent Document 1 and Patent Document 2. However, the present inventors considers that even in these methods, for example, it is difficult to make the ion collision and the spatial density distribution of the plasma uniform between the central part and the outer peripheral part of the target. In the case of the method as described in Patent Document 1, it is possible to temporally change the region where the magnetic field (line of magnetic force) is orthogonal to the electric field by rotating the magnet system (magnet), but only one magnet system is provided, and the region where the magnetic field (line of magnetic force) at a moment is orthogonal to the electric field is generated at only one position on the target. Therefore, the present inventors considers that when the enlargement of the area of substrate and the thickness reduction of the thin film to be formed are further advanced as predicted for the future, it is difficult to reduce the inhomogeneity and the film thickness nonuniformity of the thin film formed on the substrate by the method as described in Patent Document 1.
In the case of the method as described in Patent Document 2, it is possible to increase the regions where the magnetic field (line of magnetic force) is orthogonal to the electric field, by alternately arranging annular N poles and S poles, which have different radius, but the magnetic field (line of magnetic force) is not orthogonal to the electric field on the N pole and the S pole, so that the ion collision and the spatial density distribution of the plasma on the target surface above the N pole and the S pole, are made different from those on the target surface between the N pole and the S pole. Therefore, the present inventors considers that when the enlargement of the area of substrate and the thickness reduction of the thin film to be formed are further advanced as predicted for the future, it is difficult to reduce the inhomogeneity and the film thickness nonuniformity of the thin film formed on the substrate by the method as described in Patent Document 2.
That is, it is an object of the present invention to uniformize the region where the magnetic field (line of magnetic force) is orthogonal to the electric field in the magnetron sputtering system, and to facilitate the homogenization of the thin film formed on the substrate and the uniformization of the thickness of the thin film.
Other objects and novel features of the present invention will become apparent from the following description and the accompanying drawings of the specification.